Locking differential actuator assembly

ABSTRACT

A locking differential is provided for selectably locking a first axle to a second axle. The locking differential utilizes a dog clutch assembly characterized by two interlocking clutch members positioned between the differential side gears on opposing sides of the differential pinion shaft. The interlocking clutch members have face splines thereon for engaging corresponding face splines formed on the side gears. An actuating mechanism can be selectably activated to force the two interlocking members into engagement with the side gears.

This application is a divisional of U.S. patent application Ser. No.08/547,239, filed Oct. 24, 1995 now U.S. Pat. No. 5,637,049.

FIELD OF THE INVENTION

This invention relates to locking differentials for motor vehicles andthe like and, more particularly, to a selectable locking differentialfor passenger, high-performance or off-highway vehicles which can beretrofitted into an existing automotive differential casing and whichcan be actuated via a remotely controlled actuator.

BACKGROUND OF THE INVENTION

In a conventional automotive drive train, power is distributed from acentrally located power plant or engine to one or more drive wheelswhich propel the vehicle in a desired direction. Early automotive drivetrains and some modern drive trains, such as for farm and certainindustrial uses, deliver power to a single rear drive wheel through asimple clutch and chain-drive system. While this design provides arelatively simple and inexpensive drive train, it suffers from severalwell-noted drawbacks which make it unsuited for general vehicular use.

The most salient drawback is the limited drive traction or accelerationforce available from a single driving wheel. Those skilled in the artwill readily appreciate that the maximum acceleration force exerted on avehicle is limited by the traction force or friction force produced bythe driving wheel(s) in contact with the road surface. Once the staticfriction of the driving wheel on the road surface is overcome, the wheelbegins to slip and any further power delivered to the wheel isdissipated in the form of heat energy rather than as an accelerationforce exerted on the vehicle. If the drive wheel gets stuck in mud orice, the vehicle becomes disabled. For a multi-wheeled vehicle,therefore, it is desirable to deliver power to as many wheels aspossible in order to maximize traction and vehicle acceleration.

A more subtle drawback is the imbalance of torque created by theexertion of a driving force on one rear wheel, but not the other. Aspower is delivered to the drive wheel during vehicle acceleration, animbalance is created which causes the vehicle to veer or swerve in adirection away from the driven wheel. Conversely, when the drive wheelimparts a deceleration force the vehicle will have a tendency to veer orswerve toward the driven wheel. This causes undesirable vehicle handlingperformance.

To balance the acceleration and deceleration forces imparted to aconventional four-wheeled vehicle, it is desirable to distribute drivingpower over at least the front two wheels (front-wheel drive) or rear twowheels (rear-wheel drive) of a vehicle. This balances the accelerationand deceleration forces exerted on the vehicle and also increases drivetraction. For off-highway driving or driving on wet or icy pavement itmay be desirable to distribute power to all four wheels (four-wheeldrive) in order to provide maximum traction under these drivingconditions.

Modern vehicular gear trains provide balanced power distribution via adifferential gear assembly disposed between the left and right axles ofa driven pair of wheels (front and/or rear). A conventional automotivedifferential consists of a pair of opposed beveled side gears secured tothe inboard side of each half-axle and engaging a centrally disposedpair of pinion gears mounted on a common pinion shaft. The pinion shaftis rotated about its transverse axis so as to apply equal forces to eachside gear, delivering balanced power to the drive wheels. During vehiclecornering or turning the pinion gears allow the side gears to rotaterelative to one another or "differentiate" so as to accommodate arelatively higher rotational speed of the outer drive wheel and arelatively lower rotational speed of the inner drive wheel.

Most modern vehicle drive trains utilize a conventional "open"differential. An open differential always divides torque equally betweenthe opposing drive wheels. This provides optimal power delivery to thewheels under most driving conditions. However, if one wheel losestraction and starts spinning with only a small amount of torque applied,the other wheel also receives only this same small amount of torque suchthat the vehicle could easily become disabled. This problem isparticularly acute when driving in muddy off-highway conditions or onwet or icy pavement. While an open differential divides torque equallybetween the drive wheels, maximum available torque is determined by thewheel having the least resistance to turning, which is undesirable.

Designers of certain high-performance racing vehicles have longattempted to overcome this problem by providing a "solid" rear axle suchthat both rear wheels are coupled together and driven in unison. A solidaxle allows the torque on one wheel to be maintained regardless of thelevel of torque exerted on the other wheel. Unlike an open differential,a solid axle has the desirable and advantageous characteristic thatmaximum available torque is determined by the drive wheel having themost traction such that adequate driving traction can be maintained evenif one wheel slips.

While solid axles are highly desirable under certain driving conditionssuch as for off-highway or high-performance automotive racing where ahigh degree of traction is required, they can present severalundesirable drawbacks under most normal driving conditions. Inparticular, a solid axle provides no differentiation between the outerand inner drive wheels during cornering. This can cause, among otherthings, severe under-steering of the vehicle, undesirable scuffing ofthe tires and uneven tire wear as the wheels are forced to maintainuniform rolling speed even during cornering maneuvers. A solid axle canalso strain the vehicle suspension system since the axle will resistturning during cornering. These drawbacks make solid axles generallyunsuited for most vehicular uses.

Many attempts have been made to design a hybrid vehicular differentialwhich combines the traction enhancing advantages of a solid axle withthe balanced power delivery and differentiating capability of aconventional open differential. Two basic types of hybrid differentialshave been proposed--"limited slip" differentials and "locking"differentials. Limited slip differentials generally utilize a frictionplate or slip plate to transmit a portion of the torque from a slippingwheel to a non-slipping wheel. Limited slip differentials do not providethe full traction power attained using a solid axle, however, becauseonly a portion of the available torque can be transmitted to thenon-slipping wheel while still allowing for adequate differentiationunder normal driving conditions. Also, limited slip differentials arenot 100% energy efficient since a portion of the available power istypically dissipated as heat energy in the friction plate.

Locking differentials, on the other hand, utilize a releasable lockingmechanism to deliver 100% power to both wheels during straight-awaydriving, but release one wheel during cornering maneuvers so that adifferential function is achieved. See, for instance my U.S. Pat. No.5,413,015, incorporated herein by reference. Locking differentialsprovide significant traction and performance advantages overconventional solid axle or open differentials. One particularly popularlocking differential product is available from PowerTrax™ of Costa Mesa,Calif. under the trademark Lock-Right™.

The Lock-Right locking differential consists of two bi-directionalclutches which replace the pinion gears and side gears of a conventionalopen differential. Each clutch has a driving member or "driver" and adriven member or "coupler". The driver mates with its coupler to form afully locking clutch combination. When the vehicle is moving straightahead, both wheels rotate at the same speed and both clutches are fullyengaged. On the other hand, when the vehicle begins to turn, the outsidewheel starts to overrun the inside wheel. This causes the outside clutchto ratchet, allowing the wheel to rotate freely as power is diverted tothe slower moving inside wheel. As the vehicle straightens out, thewheels again rotate at the same speed and the outside clutch re-engages.This differentiating action occurs automatically for right and leftturns and in both forward and reverse directions.

While such locking differential products have been well received byoff-highway and high-performance automotive enthusiasts, originalequipment manufacturers ("OEMs") have been slow to accept such productsfor use in new vehicles. OEMs have expressed several concerns withexisting locking differentials. For example, the functioning of mostlocking differentials produces a series of clicking, ratcheting orclanking sounds during vehicle cornering as the clutch driveralternately engages and disengages the coupler. While these sounds areusually not a problem for off-highway or high-performance racing, theymay be objectionable for day-to-day driving.

Existing locking differentials can also create an under-steeringcondition during vehicle turning as power is diverted from the outsidewheel to the inside wheel. Again, while this behavior is generally not aproblem for off-highway or high-performance driving, it may beobjectionable for day-to-day driving where a more balanced powerdistribution would be preferred. OEMs are also concerned that frequentratcheting of the driver and coupler may create increased wear and tearon the differential gear assembly leading to decreased durability.

Several existing locking differential manufacturers have attempted toaddress some of these concerns by adding compensating components, suchas hold-out rings, additional pinion gears, and silencers. However,these modifications do not eliminate occasional clanking sounds, and addsignificant numbers of components representing substantial increase inboth labor and material costs. Other manufacturers offer lockingdifferentials which are selectable, such that they can be engaged ordisengaged, as desired. However, these products have many externalcomponents and are not adapted to be fitted into a standard differentialcasing, making them prohibitively expensive either as aftermarket itemsor as OEM vehicle options.

For example, ARB of Victoria, Australia offers a selectable lockingdifferential which replaces the entire differential gear assembly anddifferential casing of a vehicle. The ARB product utilizes apneumatically-actuated piston to lock one of the side gears to thedifferential casing such that up to 100% of the torque is delivered tothe other side gear through the pinion gears. Additional pinion gearsand shafts are added to carry the increased torque. An air compressor isalso required to be installed in the vehicle to produce the pressurizedair needed to operate the ARB locking differential. For retrofitinstallations, a hole must be drilled through the differential carrierand axle housing in order to introduce a pneumatic control line. Theinstallation procedure alone for installing the ARB locking assembly,pneumatic actuator and air compressor is prohibitively expensive formany automotive consumers and may, at least for retrofit applications,introduce abrasive metal particles into the differential gear assembly.

SUMMARY OF THE INVENTION

Accordingly, there is a need for a selectable locking differential thatis quiet and relatively inexpensive to manufacture and which is easilyand inexpensively retrofitted into a conventional automotivedifferential casing.

In accordance with one embodiment the present invention provides alocking differential kit adapted for assembly into a casing of anautomotive differential gear assembly disposed between a first driveaxle shaft and a second drive axle shaft for converting a conventionaldifferential gear assembly into a locking differential gear assemblywhich can be selectably actuated to lock the first drive axle shaft tothe second drive axle shaft.

In accordance with another embodiment the present invention provides alocking differential assembly for selectably locking a first drive axleshaft to a second drive axle shaft. The locking differential assemblycomprises first and second differential side gears which are angularlyfixed with respect to the first and second drive axle shafts. One ormore differential pinion gears are also provided and are operablyengaged between the first and second side gears for allowing rotationaldifferentiation thereof. A locking mechanism is adapted to selectablylock the first and second differential side gears to one another so asto provide the function of a solid axle.

In accordance with yet another embodiment the present invention providesa locking mechanism for selectably locking a first differential sidegear to a second differential side gear of an automotive differentialgear assembly. The locking mechanism comprises a pair of interlockingclutch members adapted to be installed on either side of a differentialpinion shaft. Each of the interlocking members has a face spline formedthereon adapted to selectably engage a corresponding mating face splineformed on each differential side gear. The interlocking members can bemoved into selective engagement with the first and second differentialside gears so as to prevent substantial rotational differentiationthereof, thereby providing the function of a solid axle.

In accordance with yet another embodiment the present invention providesa method for selectably locking an automotive differential gear assemblydisposed between a first drive axle shaft and a second drive axle shaft.The method comprises actuating a pair of interlocking clutch membersdisposed between a first differential side gear and a seconddifferential side gear so as to lock the side gears together, therebypreventing substantial rotational differentiation of the first andsecond drive axle shafts.

In accordance with yet another embodiment the present invention providesan actuator assembly for actuating a locking clutch mechanism disposedwithin a rotating casing of a vehicular differential. The actuatorassembly comprises an actuator rod disposed within a central bore formedaxially through a pinion shaft of the vehicular differential. Theactuator rod has one or more cam surfaces disposed thereon adapted toengage one or more corresponding actuator balls. The actuator balls aredisposed within corresponding openings formed transversely through thepinion shaft and are positioned such that when the actuator rod isdisplaced axially the cam surfaces force the actuator balls outward,thereby actuating the locking clutch mechanism.

In accordance with yet another embodiment the present invention providesa locking differential for selectably locking a first axle shaft to asecond axle shaft. The locking differential comprises a differentialcase comprising a substantially open interior portion and an outerportion comprising a ring gear adapted to be driven by a drive gearconnected to a power source. First and second differential side gearsare disposed within the interior portion of the differential case andare angularly fixed with respect to the first and second axle shafts. Apair of differential pinion gears are rotatably mounted on a commonpinion shaft and in engagement with the first and second differentialside gears for allowing rotational differentiation thereof. Each of thedifferential side gears has an inner face and an outer face. The innerface has a face spline formed thereon. A pair of interlocking clutchmembers are also provided mounted on either side of the pinion shaft.Each of the interlocking clutch members has a corresponding face splineformed on an outer face thereof adapted to engage the face spline formedon the inner face of each differential side gear. An actuator isprovided for selectably moving the interlocking clutch members intoengagement with the first and second differential side gears so as toprevent substantial rotational differentiation thereof, therebyproviding the function of a solid axle.

These and other objects and advantages of the present invention willbecome readily apparent to those skilled in the art having reference tothe following figures and accompanying detailed description of thepreferred embodiments. The following description is provided by way ofillustration only and is not to be construed as limiting in any way ofthe scope of the invention disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a four-wheel-drive au emotive drivetrain assembly showing differential units on both the front and rearaxles;

FIG. 2 is an enlarged perspective view of a conventional automotivedifferential, illustrating the carrier and housing;

FIG. 3 is a top plan cross-sectional view of the differential of FIG. 2,illustrating a conventional open differential gear assembly;

FIG. 4 is an enlarged cross-sectional view of a locking differentialgear assembly having features in accordance with the present invention,the differential gear assembly being illustrated in the unlockedcondition;

FIG. 5 is an enlarged cross-sectional view of the locking differentialgear assembly of FIG. 4 illustrated in the locked condition;

FIG. 6 is a side elevational view of a locking dog clutch assemblyhaving features in accordance with the present invention;

FIG. 7 is a plan view of the locking dog clutch assembly of FIG. 6;

FIG. 8 is a partial cross-sectional view of the locking dog clutchassembly of FIG. 7;

FIG. 9 is a partial cross-sectional view of the locking dog clutchassembly of FIG. 6;

FIG. 10 is side elevational view of the inner surface of an interlockingclutch member having features in accordance with the present invention;

FIG. 11 is a side elevational view of the outer surface of theinterlocking clutch member of FIG. 10; FIG. 11a is an enlarged view of aspline tooth as taken at line 11a--11a of FIG. 11;

FIG. 12 is a top plan view of the interlocking clutch member of FIG. 10;

FIG. 13 is a bottom plan view of the interlocking clutch member of FIG.10;

FIG. 14 is a plan view of the interlocking dog clutch member of FIG. 13rotated 90 degrees;

FIG. 15a is a top plan view of the dog clutch assembly of FIG. 7,illustrated in the unlocked condition;

FIG. 15b is a top plan view of the dog clutch assembly of FIG. 7,illustrating the camming action of the interlocking clutch members;

FIG. 16 is a side elevational view of the inner face of a lockingdifferential side gear having features in accordance with the presentinvention;

FIG. 17a is a cross-sectional view of a pinion shaft actuator assemblyhaving features in accordance with the present invention, the actuatorassembly being illustrated in the unactuated condition;

FIG. 17b is a cross-sectional view of the pinion shaft actuator assemblyof FIG. 17a illustrated in the actuated condition;

FIG. 18a is a cross-sectional view of an electromagnetic actuatorassembly having features of the present invention, the actuator assemblybeing illustrated in the unactuated condition;

FIG. 18b is a cross-sectional view of the electromagnetic actuatorassembly of FIG. 18a, illustrated in a partially actuated condition;

FIG. 18c is a cross-sectional view of the electromagnetic actuatorassembly of FIGS. 18a and 18b illustraed in the fully actuatedcondition;

FIG. 19 is a cross-sectional view of a fully assembled lockingdifferential gear assembly and electromagnetic actuator assembly havingfeatures in accordance with the present invention; and

FIG. 20 is an enlarged perspective view of a differential carrier andhousing schematically illustrating a locking differential selectorhaving features in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a typical drive train assembly 20 for afour-wheel-drive vehicle. The drive train assembly 20 includes a centraltransmission 30 for providing input power from an engine (not shown) tothe drive train. This power is distributed to front and reardifferentials 22 and 24 via front and rear drive shafts 32 and 34 and aplurality of associated universal couplings 36. It will be appreciatedby those skilled in the art that rotation of the drive shafts 32, 34causes rotation of the front and rear axles 26, 28 via the front andrear differentials 22, 24.

Each of the axles 26, 28 comprises a pair of axle shafts or half-axlesleading to outboard wheels 37. Thus, the front axle 26 comprises a rightaxle shaft 38a and a left axle shaft 38b. Likewise, the rear axle 28comprises a right axle shaft 40a and a left axle shaft 40b. The frontand rear differentials 22, 24 allow for differentiation, or unequalrotation, of the axle shafts. As is well known, when a four-wheeledvehicle is negotiating a turn, the inner and outer wheels must rotate atdifferent speeds in order to prevent scuffing of the tires. This isdesirable for most normal driving conditions and provides well-behavedvehicle performance.

FIG. 2 illustrates the outer assembly or housing of a conventionalautomotive differential. An exterior housing 52 defines a pair oflateral side tubes 54 within which are disposed the right and left axleshafts 40a,b. The housing 52 typically has a generally ring-shapedmiddle-portion, as shown, open on both front and rear sides, withcircular flanges (not shown) extending radially inward on the front andrear sides. A housing cover 58 (FIG. 1) mounts on the rear side of thedifferential housing 52 to seal the housing from dirt and debris. Acarrier 56 is mounted to the other side of the housing 52, as shown.

The carrier 56 carries a drive gear (not shown) which transmits powerfrom a drive coupling 64 to the differential gear assembly and then tothe axle shafts 40a,b. Typically, threaded holes are provided in thehousing 52 for receiving studs 50. These studs extend outward to providethreaded mounts for attaching the carrier 56 on one side and the housingcover 58 (FIG. 1) on the other. A plurality of nuts 60 secure bothelements to the housing 52 with gaskets typically provided therebetween.Alternatively, one or the other of the carrier 56 or cover 58 may bewelded to the housing 52, as is well known to those skilled in the art.The enclosure thus formed ensures a sealed lubricated environment withinwhich the differential gear assembly is housed.

FIG. 3 is a horizontal cross section of the differential 24 of FIG. 2,illustrating the differential gear assembly disposed therein. As notedabove, the generally funnel-shaped carrier 56 forms part of thelubricated enclosure for the differential gear assembly and carries thedrive gear 68 journaled with respect to the carrier 56 by a pair ofbearings 72. The drive gear 68 receives power from the engine through anassociated coupling and gear box (not shown). The teeth of the drivegear (typically hypoid or spiral) engage a corresponding bevelleddifferential ring gear 76, as shown. The ring gear 76 drives adifferential case 78 rotatably supported within the space 74 by a pairof differential bearings 80. The bearings 80 laterally surroundoutwardly extending bearing surfaces formed on the ends of thedifferential case 78, as shown.

A pair of beveled differential side gears 86a,b are rotatably supportedwithin the differential case 78, as shown. Each side gear 86a,b isconnected to the inboard end of its corresponding axle shaft 40a,b via aspline connection as is well known in the art. A pair of opposed beveleddifferential pinion gears 88 are disposed between the side gears 86a,b,as shown, such that the pinion gears 88 mesh with the bevelleddifferential side gears 86a,b. The pinion gears 88 are typically mountedon a common pinion shaft 82, as shown, the pinion gears havingthrough-bores formed therein, providing suitable bearing surfaces. Thepinion shaft 82 is secured in place within a pair of aligned apertures84 formed in the differential case 78 by a retaining pin 70. The centerof the pinion shaft 82 defines an axis 85 lying in a plane orthogonal toa common axis 87 of the axle shafts 40a,b and side gears 86a,b. Thus,the side gears 86a,b and pinion gears 88 always rotate aboutperpendicular axes.

In operation, power is delivered to the differential case 78 via thedrive gear 68. Rotation of the differential case 78 causes the pinionshaft 82 and differential pinion gears 88 disposed on the ends thereofto revolve about the common axis 87 of the axle shaft. Mating engagementbetween the teeth of the differential pinion gears 88 and opposing sidegears 86a,b transmits driving torque to each corresponding axle shaft40a,b, causing them to turn and propel the vehicle in a desireddirection. During vehicle cornering the operational coupling of the sidegears 86a,b through the differential pinion gears 88 allows relativerotation or "differentiation" between the side gears 86a,b such thatpower continues to be distributed to each of the two axle shafts 40a,bwhile allowing for variances in the rotational speed of each axlerelative to the other.

Up to this point elements common to many conventional automotivedifferentials have been described. The present invention provides animproved differential gear assembly which can be retrofitted into aconventional automotive differential casing and which can be selectablyactivated to provide a fully locked or "solid" axle or deactivated toprovide a conventional open differential. In one preferred embodiment, alocking differential kit is provided which is adapted to be retrofittedinto an existing automotive differential casing. Alternatively, alocking differential constructed in accordance with the presentinvention may be installed in a new vehicle as a standard feature orfactory option, as desired.

Locking Differential Gear Assembly

FIGS. 4 and 5 are cross-section views of a selectable lockingdifferential gear assembly 81 having features in accordance with thepresent invention. The locking differential gear assembly 81 ischaracterized by a pair of locking side gears 89a,b each having adog-tooth face spline formed on the inner face thereof. A novelinterlocking dog clutch assembly 90 is disposed within the space definedby the locking side gears 89a,b and differential pinion gears 91. Thedog clutch assembly 90 is adapted to lock the side gears 89a,b togetherwhen the locking differential 81 is activated, simultaneously lockingthe axle shafts 40a,b together.

Briefly, the dog clutch assembly 90 comprises a pair of interlockingclutch members 92a and 92b adapted to mate with one another and to eachcorresponding locking side gear 89a,b. Each interlocking clutch member92a,b has a dog-tooth face spline formed on the outer surface thereofadapted for locked engagement with the corresponding face spline formedon the inner face of each corresponding locking side gear 89a,b. A largecentral through-bore 94 is also formed in each interlocking clutchmember 92a,b for accommodating the inboard end of each correspondingaxle shaft 40a,b. The diameter of the bore 94 is preferably at leastslightly larger than the outer diameter of each axle shaft 40a,b so asto permit relative rotation between each of the interlocking clutchmembers 92a,b and the axle shafts 40a,b. Alternatively, the bore 94 maybe formed only partially through each clutch member 92a,b as needed toprovide adequate clearance between each clutch member 92a,b and eachcorresponding axle shaft 40a,b.

When the differential assembly 81 is in its unlocked position, as shownin FIG. 4, the interlocking clutch members 92a,b are biased togetheraround the pinion shaft 107 so that they clear the locking side gears89a,b, as shown. In this position the locking clutch members 92a,b arespaced apart from the adjacent inner faces of the locking side gears86a,b, as shown. In this mode, the differential assembly 81 behavesessentially like a conventional open differential, with fulldifferentiation being provided by the pinion gears 91. No clicking,ratcheting, or clanking sounds are generated by the dog clutch assembly90 since, when adequate clearance is provided to avoid contacting thelocking side gears 89a,b, the interlocking members 92a,b simply rotatewith the pinion shaft 107.

When the differential assembly 81 is in its locked position, as shown inFIG. 5, the interlocking clutch members 92a,b are biased outward so asto engage locking side gears 89a,b. The clutch members 92a,b remainengaged with one another so that the locking side gears 89a,b becomelocked to one another through the clutch members 92a,b. In this mode thedifferential assembly 81 behaves essentially like a solid axle.

Interlocking Dog Clutch Assembly

FIGS. 6-9 illustrate in more detail the preferred construction of aninterlocking dog clutch assembly in accordance with the presentinvention. FIG. 6 is a side elevational view of the interlocking dogclutch assembly of FIG. 4 looking inward from one of the locking sidegears 89a. FIG. 7 is a plan view of the interlocking dog clutch assemblyof FIG. 4 looking inward from one of the pinion gears 91.

As shown in FIG. 7, the interlocking clutch members 92a,b comprisemating halves which surround the pinion shaft 107. The interlockingclutch members 92a,b may be machined from any relatively strong grade ofalloy steel. In a particularly preferred embodiment, a 9310case-hardened steel alloy, coated with a suitable rust inhibitor, isused. Each interlocking clutch member 92a,b includes an outer face 106and an inner face 100, as shown in FIG. 7. The outer face has a splineformed thereon (FIG. 6) adapted for locked engagement with the facespline formed on the inner face of each corresponding locking side gear89a,b (FIG. 4). The inner face 100 of each interlocking member 92a,bdefines channel portions 96 which, together with the opposed channelportions on the other interlocking member, define a space or recess 98for accommodating the locking differential pinion shaft 107.

The channel portions 96 of the interlocking clutch members 92a,bpreferably diverge in a generally radially outward direction, as shownin FIG. 7. The distance across each channel portion 96 is smallest atthe intersection with the central throughbore 94, and largest at theouter periphery of the interlocking member 92a,b. Adequate clearance isprovided between the pinion shaft 107 and the channel portions 96 evenat the narrowest point, although the gap widens farther outward. Thisgenerally hourglass-shaped pinion shaft recess 98 allows for limitedrelative rotation of the interlocking clutch members 92a,b relative tothe pinion shaft 107, as will be explained later.

Four centering springs 118 are provided, as shown in FIG. 8, for biasingthe pinion shaft 107 into a central position between the respectivechannel portions 96 in the pinion shaft recess 98. Each centering spring118 is constrained to act along a defined axis by virtue of being heldwithin apertures 136. The springs 118 contact the pinion shaft 107(which is fixed with respect to the case 78) in order to center theinterlocking clutch members 92a,b relative to the pinion shaft 107. Thisensures that the interlocking members 92a,b are able to rotate at leasta slight amount in either direction from their unactuated positions.Centering springs 118 having an outer diameter of about 0.265 inches, anuncompressed length of between about 0.50 and 0.625 inches, and a springconstant of about 400 lbs/in should be suitable for most purposes. Otherspring sizes or shapes may be used while still enjoying the benefits ofthe present invention.

Each interlocking clutch member 92a,b also includes two or moreangularly spaced spring retainer pins 102, as shown in FIG. 6.Corresponding retainer springs 104 extend between pins 102 provided onopposing interlocking clutch members 92a,b, as shown in FIG. 7. In anunlocked mode, the retainer springs 104 maintain the interlocking clutchmembers 92a,b in mating contact around the pinion shaft 107, as shown inFIG. 6 and out of engagement with the side gears 89a,b. If desired, thepinion shaft 107 may be fitted within an optional rectangular alignmentblock (not shown) disposed within the recess 98 in order to bettermaintain alignment of the interlocking clutch members 92a,b duringoperation.

Interlocking Clutch Members

FIGS. 10-14 illustrate an interlocking clutch member 92a having featuresof the present invention. Preferably each clutch member 92a,b isinterchangeable with the other such that only one need be describedherein. Of course, non-interchangeable clutch members can also be used,as desired, while still enjoying the advantages and benefits of thepresent invention. It can be seen from FIG. 10 that the channel portions96 divide the interlocking clutch member 92a into two generallysemi-circular mating regions--a male region 120 and a female region 122.The male region 120 comprises a central male engagement member 124projecting above flat relief regions 126 on either side. The maleengagement member 124 is preferably formed as a truncated cylinderpartially projecting above the relief regions 126 and having a flat topsurface 125, as shown. The female region 122 comprises a central femaleengagement recess 128 disposed between two upstanding lugs 130 havingflat tops 131. When the two members 92a,b are mated, the lugs 130 of onemember contact the relief regions 126 on the other member, and visaversa.

As shown in FIGS. 15a and 15b, the male engagement member 124 is sizedto fit within the female engagement recess 128 when the two interlockingmembers 92a,b are mated together. The female engagement member 124 hascurved (preferably helical) side walls 134 adapted to slidingly engagethe curved outer surfaces of the male engagement member 124 as theclutch members are rotated relative to one another, as illustrated inFIGS. 15a and 15b. This sliding contact between the curved walls 132 ofthe male engagement member 124 and the helical-shaped side walls 134 ofthe female engagement recess 128 results in a camming action when atorque is applied across the locked clutch assembly. This camming actionforces the clutch members 92a,b outward when the differential assembly81 is in the locked condition, increasing the engagement force of eachclutch member with its corresponding locking side gear 89a,b so as toprevent disengagement of the clutch members as driving torque isapplied.

As noted above, each interlocking clutch member 92a,b comprises on theouter face 106 a dog-tooth face spline 110, as shown in FIG. 11. Theface spline 110 preferably comprises teeth 108 formed in a radialpattern disposed about a central axis of the throughbore 94.Alternatively, any other face spline configuration of straight, curvedor angled teeth may be used while still enjoying the benefits andadvantages of the present invention. As shown in FIG. 11a, each tooth108 preferably has tapered sides 112 extending from essentially flatbottom grooves 114 disposed between each tooth. The bottom grooves 114preferably are formed in a plane orthogonal to the throughbore axis ofthe interlocking member 92a,b. The tapered sides 112 of each tooth 108make a shallow angle θ with respect to the normal axis, as indicated bythe line 116. This angle θ is referred to as the pressure angle and ispreferably between about 0°-10°. More preferably, the pressure angle θis between about 5°-7°.

As noted above, the face spline 110 formed on the outer face of eachclutch member 92a,b is adapted to matingly engage a similar face splineformed on the inner face of each locking side gear 89a,b, as will befurther explained below.

Locking Side Gears

FIG. 16 is a side elevational view of a locking side gear 89a of FIG. 4looking outward from the locking dog clutch assembly 90. Preferably thelocking side gears 89a,b are interchangeable such that only one need bedescribed herein. Again, non-interchangeable locking side gears can alsobe used, as desired, while still enjoying the benefits and advantages ofthe present invention. The side gears 89a,b are preferably similar to aconventional beveled differential side gear in that they have aplurality of beveled teeth 144 and a spline 83 adapted to engage acorresponding spline 66 provided on the inboard end of each axle shaft40a,b (FIG. 3).

In addition, the locking differential side gear 86 in accordance withthe present invention has a face spline 140 formed on the inner facethereof. The face spline 140 includes a plurality of radially directedteeth 142a, 142b adapted to mate with the face spline 110 formed on theother face of each corresponding interlocking clutch member 92a,b, asdescribed above in connection with FIG. 7. The longer spline teeth 142acorrespond to each side gear bevel tooth 144, while shorter spline teeth142b are provided between the longer teeth, as shown. In the illustratedembodiment, therefore, the number of teeth 142a,b is roughly double(2n-1) the number (n) of bevel gear teeth 144. Although this arrangementis preferred, those skilled in the art will readily appreciate that awide variety of other arrangements are also possible. Thus, theparticular configuration shown should be taken as an illustrativeexample only.

Preferably, each spline tooth 142a,b has a tapered cross-section with apressure angle preferably equal to the corresponding pressure angledefined by the teeth 108 formed on the mating interlocking clutch member92a,b--preferably between about 0°-10° and, more preferably, betweenabout 5°-7°.

Actuation of the Dog Clutch Assembly

As noted above, the dog clutch assembly 90 is actuated by forcing apartthe two interlocking members 92a,b against the retainer springs 104, asshown in FIG. 5. There are many different ways to accomplish this. Thepresent invention contemplates a two-stage actuation process whichensures positive engagement of the interlocking members 92b with theside gears 89a,b. In this process, the interlocking members 92a,b arefirst urged apart a short distance into contact with the face spline 140of the locking side gears. Depending on the rotational registry betweenthe mating face splines 110 and 140, the mating clutch member andlocking side gear may immediately engage, or engagement may be delayed.In this operation, the preferred pressure angles formed by the teeth 108(FIG. 11a) and 142a,b (FIG. 16), facilitate engagement by creating asuitable gap between adjacent teeth of each mating spline at leastslightly wider than the top surface of the teeth. Because the splineteeth are required to withstand substantial stress, however, thepressure angle is preferably not too great as the teeth may taper downtoo narrow and may become over-stressed.

When the face spline 110 of one of the interlocking clutch members 92a,bmeshes with the face spline 140 of its associated side gear 89a,b, theinterlocking member will be constrained to rotate with the locking sidegear. As the two side gears 89a,b differentiate the first interlockingmember 92a,b to mesh will rotate a small amount with respect to the case78, and thus with respect to the opposite interlocking clutch member, asseen in FIG. 15b. This relative rotation between the two interlockingmembers 92a,b forces the unmeshed interlocking clutch member outwardinto engagement with its associated locking side gear 89a,b. Morespecifically, as briefly noted above, the side walls 134 defined by thefemale engagement recess 128 define a helical surface which urges themale engagement member 124 in contact therewith outward as the twomembers rotate relative to one another. The helix shape is formed onboth side walls 134 so as to urge the male engagement member 124 outwardregardless of the relative rotation between the two interlocking members92a,b. This is the second, or positive locking, step of the actuationprocess. Ultimately, the two interlocking members 92a,b are forcedoutward to lock the side gears 89a,b and the associated axle shafts40a,b.

The preferred distance each interlocking clutch member 92a,b must moveto fully engage with its associated locking side gear 89a,b isapproximately 0.080 inches. The helical surface 134 is designed so thatabout a 5.25° relative rotation of the interlocking members will forcethem apart this distance. The pinion recess 98, described above inconnection with FIGS. 7 and 8, is preferably large enough to accommodatethis degree of rotation in either direction. After engagement iscomplete, the centering springs 118 will again return the interlockingclutch members 92a,b to a centered position relative to the pinion shaft107.

Advantageously, because the locking side gears 89a,b are locked directlyto one another through the locking dog-clutch 90, the torque from thedrive gear 68 is communicated from the pinion gears directly to thelocking side gears 89a,b in parallel. Thus, the shear force exerted oneach pinion gear 91 is evenly split between each locking side gear, asillustrated by the arrows in FIG. 5, such that the pinion gears will notbe over-stressed even when the differential is in its locked condition.Of course, additional pinion gears can be added in order to provide aneven more robust differential, as desired.

Pinion Shaft Actuator Assembly

Those skilled in the art will appreciate that a wide variety of actuatormechanisms may be used to selectively activate or deactivate the lockingdifferential described herein. The actuator mechanism may comprise anyvariety of pneumatic, hydraulic, electromagnetic or mechanicaltransducers which respond to an actuating signal to produce a desireddisplacement of the interlocking clutch members 92a,b, the invention notbeing limited to any particular device.

FIGS. 17a and 17b illustrate, by way of example only, one possibleembodiment of a pinion shaft actuator assembly 148 comprising a portionof a locking differential actuator having features of the presentinvention. The assembly 148 generally comprises a hollow pinion shaft107, an actuating rod 150, an actuating cable 152 attached to one end ofthe rod, and a plurality of spring-loaded actuating balls 154 adapted toact against compression springs 156. The actuating rod 150 is adapted toslide freely within an elongated bore 158 formed through the pinionshaft 107. The rod 150 preferably includes two pairs of opposed conicalcam depressions 160 arranged as shown, each depression having anincluded angle of between about 75° and 120°, and more preferably, about100°. The two cam depressions 160 in each pair are opposed across thelongitudinal axis 85 of the actuating rod 150, terminating atapproximately the rod center, as shown.

Actuating balls 154 and actuating springs 156 are disposed adjacent eachcam depression and in mechanical communication therewith. The springs156 act between the balls 154 and the interlocking clutch members 92a,b,as shown. As seen in FIG. 17a, the actuating balls 154 reside largelywithin the depressions 160 when the actuating rod 150 is in itsnon-actuated position. This position-corresponds to an unlocked state ofthe dog clutch assembly 90 (FIG. 4), with the two interlocking members92a,b being held together in close proximity about the pinion shaft 107.

FIG. 17b shows the actuating rod 150 in its fully actuated positionaxially shifted from the position of FIG. 17a. Those skilled in the artwill appreciate that as the rod 150 is moved axially, the camdepressions 160 move out of registry with the through holes 162 thusforcing the balls 154 outward in a camming action. As the balls 154 moveoutward, the actuating springs 156 compress and impart an outward forceto the interlocking clutch members 92a,b. Eventually, the outward forceof the four actuating springs 156 acting in combination overcomes theinward force of the retaining springs (not shown) holding theinterlocking members 92a,b together. The interlocking members 92a,b arethus forced apart and into engagement with the side gears 89a,b, asdescribed above in connection with FIG. 5.

The rod 150 may be displaced via an actuating cable 152. The cable 152should be sufficiently strong to withstand tensile forces of betweenapproximately 10-50 lbs., and more preferably about 20 lbs. A 0.050 inchdiameter aircraft cable, for example, should be suitable for mostpurposes. A flexible elongated member, such as a tape, may also be used,if desired. Advantageously, a tape actuator can be made thinner toreduce the clearance area required at the end of the pinion shaft 107. Atape having a thickness of about 0.008 inches should be suitable formost purposes. The actuating cable 152 can be attached to the actuatorrod 150 using any one of a number of attachment techniques well known inthe art, such as crimping, soldering or looped connection.

To accommodate the actuating cable or tape 152 one end of the pinionshaft 107 includes a cutout portion 202 leading to the inner bore 158 inwhich a pin 204 is positioned with a pulley 206 journaled thereon. Theactuating cable 152 extends longitudinally through the bore 158 and isdirected 90° around the pulley 206, as shown. Of course, a roundedcorner formed at the end of the bore 158 could also serve to redirectthe cable 152 and obviate the need for a pulley. Alternatively, theactuating rod 150 could be displaced using a hydraulic or pneumaticforce, or it could be rotatably actuated, as desired. An optionalshoulder 151 may be formed within the elongated bore 158, as desired, inorder to prevent hyperextension of the actuating rod 150.

Electromagnetic Actuator

FIGS. 18a-c illustrate one possible embodiment of an electromagneticactuator 200 for activating the dog clutch assembly 90 of the presentinvention. For purposes of illustration, the various actuator elementsare shown outside of the differential carrier 56 and casing 78. Ofcourse, the actuator would normally be assembled within the differentialcarrier or housing, although that is not necessarily required. Also, itshould be noted that the present electromagnetic actuator 200 isdescribed in conjunction with the pinion shaft actuator assembly 148 ofFIGS. 17a and 17b. Again, those skilled in the art will readilyappreciate that many different actuating devices may be used inconjunction with the electromagnetic actuator as disclosed and describedherein to activate the locking dog-clutch assembly of the presentinvention.

The actuator 200 basically comprises an electromagnetic ring 232 and amovable plate 218 adapted to be selectably drawn toward the ring 232 inresponse to an electromagnetic field generated thereby. A guide member210 rigidly attaches to the end of the pinion shaft 107, as shown, ordifferential case 78 (not shown) and supports a shoe 208 which islinearly constrained to slide along the guide member 210. The actuatingcable 152 is attached to one end of the shoe 208, as shown, using anyone of a number of well-known attachment techniques, such as soldering,crimping or looped connection. Preferably the shoe 208 includes atension adjustment mechanism (not shown) in order to adjust the tensionexerted on the actuating cable 152. It will be understood that theentire assembly comprising the pinion shaft actuator assembly 148, guidemember 210, cable 152 and shoe 208, rotates with the differential case78.

The shoe 208 includes a base portion 212 slidably retained within theguide member 210, as shown, and a pair of runners 214, 226 slidablyretained within corresponding circular grooves 216, 224 formed in themovable plate 218. The movable plate 218 is rotatably fixed with respectto the electromagnetic ring 232. When the ring 232 is energized theplate 218 is drawn toward the ring 232. This causes the shoe 208 also tobe drawn toward the plate 218 creating a tensile force on the actuatingcable 152, actuating the locking dog-clutch assembly substantially asdescribed above in connection with FIGS. 17a,b.

The movable plate 218 is preferably a ring-shaped member formed of asteel or other ferrous material. The plate 218 has a generally flatouter rim portion 220, as shown, and a relatively thicker inner portion222, which includes the circular grooves 216, 224. The movable plate 218also includes a plurality of apertures 228 extending axially through theouter rim portion 220. Only one of the apertures 228 is shown in FIG. 17for purposes of illustration. There are preferably at least three ormore such apertures substantially evenly spaced around the periphery ofthe movable plate 218. The apertures 228 each receive pins 230 axiallyextending from the electromagnetic ring 232. Each pin 230 includes asmall transversely oriented stop pin 234 fixed therein having a lengthsufficient to prevent the plate 218 from disengaging from theelectromagnetic ring 232. Alternatively, any number of other retainingmeans well known in the art may be used to retain the plate 218 in aposition adjacent to the electromagnetic ring 232, as shown.

A coiled return spring 238 is preferably provided between theelectromagnetic ring 232 and the movable plate 218 in order to bias themovable plate 218 away from the electromagnetic ring 232. The spring 238is preferably adapted to fully collapse upon itself so that itscompressed length is minimal. The spring 230 preferably lies within anannular recess 236 formed in the plate 218. In a preferred embodiment,the plate 218 and ring 232 define a gap 235 of between about 0.125 to0.150 inches when the ring is not energized, and a gap 235 of betweenabout 0.0 to 0.030 inches when the ring 232 is energized.

The electromagnetic ring 232 comprises a rear ring plate 240 having anangled inner wall 242 extending outwardly toward the movable plate 218.The combination of the ring plate 240 and the angled wall 242 define anannular space within which an electromagnetic coil 244 is disposed, asshown. An outer annular cover 246 surrounds the coil 244 in order tolimit dispersion of the electromagnetic field generated thereby. Themagnetic field path around the coil is interrupted by a small annulargap 237 approximately 0.062 to 0.150 inches across, as shown. This gap237 directs the magnetic field through the adjacent plate 218, therebydrawing it toward the ring 232 when it is energized.

In one particular preferred embodiment, the gauge of wire used for thecoil 244 is designated 20H or 21H, and the coil 244 has approximately220 turns around the ring 232. The mean turn length (MTL) isapproximately 14 inches, the mean path length (MPL) is approximately 2inches, and the mean surface area is approximately 8 square inches. Thecoil is adapted to be energized by a 12 VDC, 4-Amp input actuationsignal applied across the coil 244 from the input terminal 48 to ground.This creates a maximum holding force of about 28 lbs with the gapbetween the electromagnetic ring 232 and movable plate 218 being about0.030 inches. This holding force will decrease somewhat upon heating ofthe apparatus, but the present configuration facilitates closure of thegap 35 between the movable plate 218 and electromagnetic ring 32, aswill be described in more detail below.

Those skilled in the art will appreciate that when the coil 244 isenergized, a magnetic attraction occurs in the gap 235 between themovable plate 218 and the ring 232. The shoe 208 resists the movement ofthe plate 218 by virtue of its connection to the actuating rod 150 whosemovement is resisted by the spring loaded balls 154. Because of thesmall space available within the differential housing, the size of thecoil 244 is limited. In fact, the magnetic actuating force required todraw the plate 218 and the shoe 208 is larger than can be created by thecoil 244, at least at the maximum gap distance existing between plates218 and 232, as shown in FIG. 18a.

However, when the coil is energized the magnetic field created therebywill initially draw a portion of the plate 218 opposite the shoe 208,pulling that portion of the plate toward the ring 232, as shown in FIG.18b. As that portion of the plate 218 opposite the shoe 208 approachesand eventually contacts the ring 232, the attraction force increasesexponentially such that the edge of the plate proximate the initialcontacting portion will also be attracted toward the ring 232 withincreasing force. Ultimately, the portion of the plate in contact withthe ring 232 will work its way around the periphery of the plate 218 ina cascading effect until the entire plate 218 is in contact with thering 232, as shown in FIG. 18c. This will eventually pull the shoe 208toward the ring 232, displacing the actuating rod 150 via the cable 152,and thereby actuating the locking dog-clutch assembly 90 as describedabove. To accommodate this mode of actuation, the holes 228 formed inthe outer rim portion 220 of the plate 218 are preferably sized slightlylarger than the pins 230 so that the plate 218 is capable of pivoting asshown in FIG. 18b.

FIG. 19 is a cross-sectional view of a fully assembled lockingdifferential and actuator assembly having features of the presentinvention. The electromagnetic actuator 200 is mounted coaxially withthe differential case 78, as shown. For some differentials, such asC-clip differentials, the pinion shaft must be installed last. This canpresent an installation problem where a retainer pin 70 is required tosecure the pinion shaft to the differential casing, since access may beprevented once the actuator 200 is installed. To accommodate finalassembly of the pinion shaft 107 in such differentials, a slot 261 maybe formed in one end of the pinion shaft 107 so as to allow it to beslipped over the assembled retainer pin 70. A retainer cap 263 can thenbe fastened via screws 265 to the end of the pinion shaft 107 in orderto secure the pinion shaft in place. These screws 265 are readilyaccessed by rotating the differential case 90 degrees from the positionillustrated.

Locking Differential Selector

The locking differential of the present invention is preferablyselectable, as noted above, so as to enable an operator of a vehicle toselectably lock the axle shafts together by activating a remoteactuator, preferably located within the vehicle cockpit or passengercompartment. Persons skilled in the art will readily appreciate thatvarious means may be used for selectably actuating a lockingdifferential having features of the present invention.

FIG. 20 illustrates one possible embodiment of a locking differentialselector having features of the present invention. The illustratedembodiment includes a switch 44 and an indicator 49 connected between avehicle battery 42 and an electromagnetic differential actuator, such asdescribed above in connection with FIGS. 18a-c. The switch and indicatorare preferably mounted on the dashboard of the vehicle such that theycan be easily operated by the driver whenever added traction is desired.An optional fuse 46 is connected in series between the switch andbattery 42, as shown, in order to limit the maximum current delivered tothe system in the even of a short circuit.

An elongated conductor 48 extends from the switch 44 into thedifferential housing 52 where it connects to a portion of anelectromagnetic differential actuator, such as the coil 244 shown inFIGS. 18a-c, the other end of the coil 244 being connected to ground.When the switch 44 is closed, current flows from the battery, though theconductor 48, energizing the coil 244, activating the lockingdifferential. The indicator 49 is also energized indicating that theaxles 40a,b are locked. Such selectability allows the present inventionto be used in dual-use vehicles, such as, for example vehicles used forboth street and off-highway use, without compromising either drivabilityor traction.

To connect the conductor 48 to an electrically operable actuatordisposed within the differential housing 52, a hollow stud 50' ispreferably provided through which the conductor 48 may pass. Threadedholes on either the front or rear side of the housing 52 may receive thestud 50'. The conducting wire 48 then extends through the hollow studinto the housing 52 and into communication with the coil 244.Optionally, the stud 50' may enclose an electrical coupling or otherelectrical interface in order to facilitate easier installation, asdesired.

Advantageously, the hollow stud 50' can also be used for other types ofdifferential actuators such as pneumatic, hydraulic, or mechanicalactuators. For instance, a small pneumatic line can be introducedthrough the bore of the stud 50' into communication with a pneumaticactuator. Moreover, the hollow stud 50' allows introduction of anexternal actuation signal into the differential housing 52 withoutrequired drilling or other machining operations which may introduceundesirable debris into the sealed differential housing 52. Significanttime and costs savings can also be realized, as no special tools orskills are needed to complete the installation.

Although this invention has been described in terms of certain preferredembodiments, other possible embodiments will be readily apparent tothose of ordinary skill in the art. Accordingly, the scope of theinvention disclosed herein is intended to be defined only by the claimsthat follow.

What is claimed is:
 1. An actuator assembly for actuating a lockingclutch mechanism disposed within a rotating casing of a vehiculardifferential, said actuator assembly comprising:an actuator rod which isdisposed and can be displaced within a central bore formed axiallythrough a pinion shaft of said vehicular differential, said actuator rodhaving one or more cam surfaces disposed thereon; at least one followercoupled to said actuator rod such that when said actuator rod isdisplaced, said cam surface engages and forces said follower outward,thereby transmitting a corresponding outward actuator force to saidlocking clutch mechanism; a cable that is coupled to said actuator rod;and, an actuator that is attached to said cable and located outside therotating casing, said actuator is actuated to displace said cable andsaid actuator rod.
 2. The actuator assembly of claim 1 wherein said camsurfaces are distributed axially along said actuator rod.
 3. Theactuator assembly of claim 1 wherein said cam surfaces are formedcircumferentially at one or more locations along said actuator rod. 4.The actuator assembly of claim 1 wherein said actuator includes anelectromagnetic actuator ring.
 5. The actuator assembly of claim 1wherein said actuator includes a mechanically, hydraulically orpneumatically operable plate.
 6. The actuator assembly of claim 1wherein said actuator includes an electric solenoid.
 7. The actuatorassembly of claim 1 wherein said follower is an actuator ball.
 8. Theactuator assembly of claim 1 further comprising a spring which biasessaid follower into said actuator rod.